This whole subject regarding MSTS vs RW vs RS etc etc is all rather subjective as it all depends on what hardware you have, what routes you use and who's stock you drive.
Ive had MSTS since it was released in the USA c2001 and at the time it was the first train sim (that I recall) aimed at the current market and was far more advanced and eye pleasing than what was then currently available.
Of course alot as come along in the 9 years or so since it was released and the lack of basic features such as TPWS, AWS and an intelligent signalling system all count against it. However there are some real gems out there (and still to come) and providing you have the setup to run them, routes like MT's GE or the freeware Dorest Coast route look brilliant. But taking into account the time difference between the different makes of train sim it stands to reason why there would be deficiencies between them.
MSTS was effectively first gen where as the later sims were able to later build on top of MSTS's success and had plenty of community support during production.
I did buy Rail Simulator when it was released and I had high hopes for it, however I soon found out that allthough it remedied some of the faults of MSTS, it contained alot of its own and I personly found the visual aspect of RS very garish and hard on the eyes....it was soon uninstalled and consigned to a dusty box! I have seen nothing that would persuade me to buy RW either.
As for the physics, well I hate to break it to you but no commercial train sim (certainly nothing current) will come close to the real thing!
I've not used rail simulator but I do have a copy of it and it does seem better
If you have not used RS then what qualifies you to say it seems better?